1. Field of the Invention
This invention relates generally to electronic communications, and, more particularly, to data constructs for representing and manipulating communication protocols.
2. Description of Related Art
A universal bus test instrument has recently been developed for exercising a wide variety of serial busses that operate with different interface specifications and protocols. U.S. patent application Ser. No. 10/325,070, entitled “Universal Approach for Simulating, Emulating, and Testing a Variety of Serial Bus Types,” describes certain aspects of this instrument, and is herein incorporated by reference. The incorporated application and the instant application are both based on provisional applications that were filed on the same day. Neither application is prior art to the other.
The incorporated patent application defines the protocol and behavior of a generic serial bus through the use of a “bus model.” As described, the bus model breaks down a serial bus protocol into separate generic layers that are common to all busses. For any particular target bus, the bus model expresses the target bus protocol in terms of the generic layers, and assigns bus-specific attributes to each generic layer. The bus model thus forms an abstract representation of the target bus protocol in terms of the generic layers.
FIG. 1 shows a block diagram of the bus model 100. The layers of the bus model include, for example, frames (112/132), messages (114/134), words (116/136), fields (118/138), symbols (120/140), sequences (122/142), encoding (124/144), and timing (126/146).
Prior bus test instruments have been primarily bus-specific. Instruments have been designed for exercising one or more particular types of busses but were not usable for exercising other types of busses. Consequently, the communication constructs that these instruments used included only the structures needed for communicating with the specifically supported bus. They were not adaptable for other types of busses.
FIG. 2 shows a typical communication construct used by a bus-specific test instrument of the prior art. For illustrative purposes, a communication construct for a MIL-STD-1553 bus test instrument is shown. The instrument supports a set of bus-specific message types 210. The message types 210 prescribe high level operations that can be conducted on the target bus. For the 1553 bus, these message types include, among others, a Bus Controller to Remote Terminal message type (BC-RT), a Remote Terminal to Bus Controller message type (RT-BC), and a Remote Terminal to Remote Terminal message type (RT-RT).
Each of the message types 210 consists of words. In general, the target bus specification prescribes a set of word types for performing various bus operations. For the 1553 bus, three distinct word types 212 are provided: Command Word, Data Word, and Status Word.
Words consist of fields. The identities and locations of fields within words are fixed by the definition of the target bus. As shown in FIG. 2, a 1553 Command Word 216 consists of six fields 214. These fields include, as defined by the 1553 standard, Sync, RT Address, Transmit/Receive, SubAddress Mode, Data Word Count/Mode Count, and Parity.
The bus-specific constructs of the prior art each support message types and word types needed for exercising a particular target bus. They are generally limited, however, to the protocols of the respective target busses. They do not provide users with a way of defining different sets of message types or word types for different types of busses. What is needed is a more flexible way of defining bus communication.